The structure of Fe-Si alloy in Earth's inner core

Shigehiko Tateno, Yasuhiro Kuwayama, Kei Hirose, Yasuo Ohishi

Research output: Contribution to journalArticle

33 Citations (Scopus)

Abstract

Phase relations of iron-silicon alloy (Fe-6.5 wt.% Si and Fe-9 wt.% Si) were investigated up to 407 GPa and 5960 K in a laser-heated diamond-anvil cell, which likely covers the entire pressure and temperature conditions of the Earth's inner core. Synchrotron X-ray diffraction measurements show that Fe-9 wt.% Si with a hexagonal close-packed (hcp) structure is stable to 4800 K at 330 GPa, corresponding to the pressure at the inner/outer core boundary, and decomposes into a mixture of Si-poor hcp and Si-rich CsCl-type (B2) phases at higher temperatures. We also found that the solubility of silicon in solid iron is relatively insensitive to temperature, decreasing from 9 to >6.5 wt.% over a range of 1500 K at 70 GPa. These suggest that the inner core is composed solely of the hcp phase, when the silicon content is up to 7 wt.% that likely accounts for the inner core density deficit as well as for the Mg/Si ratio and the Si isotopic composition of the mantle. Additionally, the present experiments demonstrate that the incorporation of silicon in iron expands the stability of hcp with respect to that of fcc.

Original languageEnglish
Pages (from-to)11-19
Number of pages9
JournalEarth and Planetary Science Letters
Volume418
DOIs
Publication statusPublished - May 5 2015
Externally publishedYes

Fingerprint

inner core
Silicon
silicon
Earth (planet)
Iron
iron
Silicon alloys
Diamond
Iron alloys
Synchrotrons
silicon alloys
diamond anvil cell
Temperature
outer core
iron alloys
Solubility
anvils
X ray diffraction
synchrotrons
Earth mantle

Keywords

  • Diamond-anvil cell
  • High pressure
  • Inner core
  • Iron-silicon alloy

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

Cite this

The structure of Fe-Si alloy in Earth's inner core. / Tateno, Shigehiko; Kuwayama, Yasuhiro; Hirose, Kei; Ohishi, Yasuo.

In: Earth and Planetary Science Letters, Vol. 418, 05.05.2015, p. 11-19.

Research output: Contribution to journalArticle

Tateno, Shigehiko ; Kuwayama, Yasuhiro ; Hirose, Kei ; Ohishi, Yasuo. / The structure of Fe-Si alloy in Earth's inner core. In: Earth and Planetary Science Letters. 2015 ; Vol. 418. pp. 11-19.
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